With the demands in speeding-up, miniaturization or the like of copy machines and laser printers in the recent years, various external additives are used for the purpose of improving fluidity or triboelectric chargeability of a toner.
For example, JP-A-2010-20024 (US-A-2010-009282) discloses that a toner containing a composite oxide having a core-shell structure in which a core portion contains titanium oxide and a shell portion contains silicon oxide, wherein titanium oxide is contained in an amount of from 80 to 95% by weight serves to suppress background fogging or soiling of a charging roller.
JP-A-2002-182424 discloses that a toner containing fine metal oxide particles having a core-shell structure in which a core layer is made of a metal oxide selected from titanium dioxide, aluminum oxide, and zinc oxide, and a shell layer is made of silica, the fine metal oxide particles having an average particle size of from 10 to 30 nm and a degree of spherocity of from 1 to 1.3 is free from background fogging, faded print, and filming and the like, and has excellent durability, thereby exhibiting a high optical density.
JP-A-2004-177747 discloses that a toner containing silica-coated metal oxide particles having a core-shell structure in which a core layer is made of a metal oxide selected from titanium dioxide, aluminum oxide, and zinc oxide, and a shell layer is made of silica, and fine silica particles having a volume-average particle size of from 5 to 20 nm, has excellent cleanability and gives excellent image quality.
WO 2009/084184 (US-A-2010-330493)discloses a toner containing surface-modified, fine composite oxide particles comprising silica-titania composite oxide particles produced by a vapor phase method subjected to a surface treatment has a small change in triboelectric charges with the passage of time.
JP-A-Hei-8-292598 discloses that a toner containing particles comprising fine inorganic particles of which primary particles have an average particle size of from 30 to 100 nm, hydrophobically treated with a dimethyl silicone oil, the particles having a carbon content ascribed to the dimethyl silicone oil in the particles of from 3.1 to 6.0% by weight has excellent developability, transferability and stability with the passage of time, and the publication describes that there is a correlation between the carbon content and phenomena so-called “characters containing non-printed spots.”
JP-A-Hei-9-204065(U.S. Pat. No. 5,695,902) discloses that a toner containing an inorganic fine powder (A) treated with at least a silicone oil, and an inorganic fine powder (B) containing a composite metal oxide one of which constituent is at least Si, and having a weight-average particle size is from 0.3 to 5 μm has excellent developing stability, high transferability and sleeve coatability under various environmental conditions, and gives high image quality even upon durability printing for numerous sheets, and the publication discloses that the inorganic fine powder (A) treated with the silicone oil is externally added to toner particles, whereby phenomena so-called a “hollow character” can be prevented over a long period of time.